2-(Pyrrol-1-yl)-imidazoleamines having antihypertensive effectiveness are known from U.K. Pat. No. 1408362. 3-Hydrazinopyridazines and 4-hydrazino-phthalazines having antihypertensive activity are broadly described in the pharmaceutical literature (see Progress in Drug Research, Vol. 20, pages 203-205, edited by E. Jucker, Birkhauser Verlag Basel, 1976).
The prior literature teaches that blocking of the terminal nitrogen of hydrazine moiety of the 4-hydrazino-phthalazines through chemically stable substituents such as alkyl or aryl groups leads to virtually inactive compounds (see Progress in Drug Research, Vol. 4, page 332, edited by E. Jucker, Birkhauser Verlag, Basel, 1962).